Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$42.45	6.236%	$45.0972	$45.10	$45.10	$45.10
Purchase #2	$172.74	11.629%	$192.8279	$192.83	$192.85	$192.80
Purchase #3	$222.59	12.624%	$250.6898	$250.69	$250.70	$250.70
Purchase #4	$159.80	9.142%	$174.4089	$174.41	$174.40	$174.40
Purchase #5	$87.96	5.737%	$93.0063	$93.01	$93.00	$93.00
Purchase #6	$203.92	9.473%	$223.2373	$223.24	$223.25	$223.20
Purchase #7	$49.69	5.185%	$52.2664	$52.27	$52.25	$52.30
7 purchase totals =	$939.15		$1,031.5338	$1,031.55	$1,031.55	$1,031.50